OK lets tackle these one at a time ;D
Explorer (known vista problem)
From the Start menu, select all programmes, accessories
then right click the command prompt and run as administrator
In the Open field, type sfc /scannow (Note: There is a space between sfc and /scannow)
Select the OK button.
Follow the prompts throughout the System File Checker process.
Reboot the computer when System File Checker completes.
For Avast it sounds like a repair is needed
Go to control panel - programs and features
Select Avast
Several options will appear select repair
Malwarebytes uninstall via programs and features
Run this tool http://www.malwarebytes.org/mbam-clean.exe
Then download and install a fresh copy
http://img233.imageshack.us/img233/7729/mbamicontw5.gif
from Here.